The present invention relates to an optical disk device which performs recording, deletion and reading upon an optical disk which has a plurality of recording layers, and in particular relates to an optical disk device which performs layer jumping.
From the prior art, optical disk devices which perform recording, deletion, and replay of information to and from optical disks having several recording layers are per se known and have been generally widespread. Such optical disks, for example, may be single sided two layer type Blu-ray disks or two layer type DVDs.
With such a two layer type optical disk, recording, deletion, and replay of information can be performed to and from a first recording layer or a second recording layer. And a cover layer is formed upon such an optical disk, so as to cover over the information recording surfaces on both recording layers. Such a cover layer is a transparent layer of a predetermined thickness, and protects the information recording surfaces of the recording layers. With such an optical disk device, laser light of reading power, recording power, or deletion power is irradiated upon the information recording surfaces of the recording layers via this cover layer. By doing this, reading, recording, or deletion of image data and audio data to and from such an optical disk may be performed with such an optical disk device.
Furthermore, with such an optical disk device, during this reading or recording or deletion, an objective lens included in the pickup is shifted in the direction towards and away from the information recording surfaces of the optical disk, on the basis of a focus error signal which is generated from the laser light reflected from the disk, and focusing servo is performed in order to focus the laser light upon the information recording surface of any desired layer of the optical disk. Moreover, such an optical disk device sometimes performs so-called layer jumping, in which the pickup transitions from a state in which it is performing reading, recording, or deletion upon a first recording layer, to a state in which it performs reading, recording, or deletion upon a second recording layer. Conversely, the optical disk device also sometimes performs layer jumping in the reverse direction as well, in which the pickup transitions from the second recording layer to the first recording layer.
Now, during this layer jumping, due to the shifting from the first recording layer to the second recording layer or the shifting from the second recording layer to the first recording layer, the thickness of the above described cover layer varies. Because of this, the value of spherical aberration also varies. Spherical aberration is a phenomenon in which the focal point of the laser light is not imaged at a single point upon the optical axis, but is imaged while deviating in the depth direction. Because of this the problem arises that, since the focus upon the information recording surface spreads out into a disk, accordingly the sensitivity for reading information or the accuracy for recording or deleting information is deteriorated, which is most undesirable.
Thus, with such an optical disk device according to the prior art, a correction lens for correcting spherical aberration is provided in the optical path of the laser light. And, during layer jumping, this optical disk device sets the correction lens to an intermediate position corresponding to an intermediate value between two optimum correction values which are calculated in advance for each of the first recording layer and the second recording layer. When performing layer jumping, for example, from the first recording layer to the second recording layer, the optical disk device turns focusing servo upon the first recording layer to OFF. And, when the layer jumping has been completed, this optical disk device turns the focusing servo upon the second recording layer to ON, and starts recording, reading, or deleting information to or from the second recording layer.
It should be understood that a focusing control device for a pickup is proposed in Japanese Laid-Open Patent Publication 2003-077142.
However, when setting the correction lens to the above described intermediate position, sometimes the balances between the upwards and downwards amplitude of the waveform of the focus error signal for the first recording layer or the second recording layer are extremely lopsided. Since these amplitudes mean the ranges over which focusing servo is possible, at a recording layer for which the balance is lopsided, there is a possibility that the focusing servo may become lost directly before the layer jump, or that it may not be possible to turn the focusing servo to ON directly after the layer jump. If in this way the focusing servo is lost or cannot be turned to ON, then the recording, reading, or deletion of information to or from the optical disk becomes interrupted, which is very undesirable.
Accordingly, with such a prior art type optical disk device, there has been a problem of interruption of recording, deletion, or reading of information directly before layer jumping, or directly after layer jumping.
The present invention has been conceived in order to solve this type of problem with the prior art, and its object is to provide an optical disk device, with which interruption of recording, deletion, or reading of information directly before layer jumping, or directly after layer jumping, is prevented.